Study On Silicon-based Photonic Modulation Devices And System For Analog Optical Link

Integrated microwave photonics is a current research hotspot.The main research content is to employ photonic integration technology to integrate microwave photonics system,that is constructed by traditional discrete optical devices,onto photonic chips.Its main functions include the generation of microwave and millimeter wave signals in the optical domain,and the transmission,processing and detection of microwave photonic signals in the optical domain.The use of photonic integration technology reduces the volume of the traditional microwave optical subsystem,the power consumption of the system,and improves the stability and reliability of the system.At present,the photonic integrated material system mainly includes indium phosphide(InP),silicon nitride(SiN)and silicon-on-insulator(SOI).Compared with InP and SiN,the SOI material system has the advantages of CMOS compatibility,high integration,and support for photoelectric monolithic integration.Therefore,silicon-based microwave photonic integration technology has great development potential.The silicon-based integrated microwave photonic chip mainly includes the following devices:silicon-based lasers,silicon-based modulators,silicon-based delay lines,and silicon germanium photodetectors.One of its most representative applications is a phased array radar based on a silicon-based true delay beamforming network.This thesis will conduct systematic theoretical and experimental research on the two most important control devices in the silicon-based integrated microwave optical subsystem—modulators and delay lines.According to the requirements of microwave photonic links for large dynamic range and high link gain,the nonlinear generation mechanism of silicon-based modulators and optical domain linearization methods are studied;low-loss and high-precision silicon-based true time delay chips are developed.According to its characteristics,a low-intrusive delay state monitoring method has been developed.On this basis,the prototype of a two-dimensional phased array radar receiver based on a silicon-based true time delay line has been developed,and the system has been tested.Based on the above research content,the work and innovations completed in this thesis include:1.For the most widely used silicon-based carrier-depleted Mach-Zehnder Modulator(MZM),this thesis first established a strict silicon-based PN junction electro-optic modulation model.We employ this model to analyze the nonlinear theories of the parallel and series silicon-based MZM in detail.On this basis,we systematically compared the comprehensive performance of these two high-linearity silicon-based modulators.Finally,according to the theoretical analysis results,we designed a highly linear silicon-based carrier depletion modulator and taped it out at IMEC.2.We conducted performance tests on the designed high linear modulator.For the silicon-based parallel MZM,we set the two sub-MZM bias points at two orthogonal points with opposite polarities.By controlling the optical power and RF power distribution ratio of the two sub-MZMs,the third-order nonlinearities generated by the two sub-MZMs cancel each other out.After testing,the working bandwidth of this device is 40 GHz.When the RF input frequency is 1/10 GHz,the 3^rd spurs-free-dynamic-range(SFDR)reaches 123/120 dB·Hz^6/7.This performance is currently the highest level of optical domain linearization of silicon-based modulators.For the silicon-based series MZM,we only need to adjust the RF power distribution ratio of the two sub-MZMs to achieve optical domain linearization.The working bandwidth of the device reaches 55 GHz,and when the RF input frequency is 1/10 GHz,the SFDR reaches 109.5/100.5 dB·Hz^2/3.3.In this thesis,a theoretical analysis model of the micro-ring modulator(MRM)nonlinearity is established.Moreover,the relationship between the modulation nonlinearity of MRM,the quality factor Q and operating wavelength is systematically analyzed.Theoretical calculation results show that the linearity of MRM can be improved by reducing the Q value of MRM while adjusting the wavelength of the optical carrier.The experimental results show that when the RF input signal is 1/10GHz,the optimal linearity of a silicon-based MRM with a Q value of 11000 is only98.5/90.6 dB·Hz^2/3.Compared with an MRM with a Q value of 5880,its best linearity is as high as 104.3/94.7 dB·Hz^2/3.This performance has reached the highest level of current linearization of the silicon-based MRM in optical domain.4.This thesis proposes and experimentally verifies for the first time that the silicon-based parallel MZM can realize the nonlinearity compensation of the RF signal in optical domain.At a modulation frequency of 10 GHz,when the 3^rd carrier to distortion ratio(CDR)of the input RF signal is 40/50 dB,the CDR of demodulated RF signal is increased to 45/72 dB after the optical-domain nonlinearity compensation.5.According to the requirements of the overall department for the two-dimensional phased array radar receiver,we designed and prepared a 4-channel 7-bit true delay line based on the optical switch path switching structure.The longest channel total delay is 676 ps.This delay line uses a stretched silicon waveguide as the delay waveguide,and its insertion loss is 0.01 dB/10 ps.In addition,its switch extinction ratio is 50 dB,and its power consumption is about 28 m W.In order to reduce the optical loss introduced by the monitoring unit(silicon-based directional coupler+silicon germanium photodetector),we proposed a method for monitoring the state of the optical switch in which the monitoring unit and the optical attenuator are alternately arranged at intervals,and designed targeted feedback control algorithm.6.Aiming at the integration trend of microwave photonic two-dimensional phased array radar,we designed and developed a new type of two-dimensional phased array radar receiver using the multi-channel delay line designed above.For phased array antennas with a scale of N?N,traditional beamforming networks require N² types of silicon-based delay lines.In contrast,this method introduces the optical wavelength division multiplexing technology,and only requires N/2 types of silicon-based delay lines,thereby reducing the system cost.Based on this solution,we developed the first prototype of an 8?8 microwave photonic phased array radar receiver based on a silicon-based integrated true delay line,and for the first time realized the full link verification from the array antenna to the signal processing.After system testing,the prototype has a working range of 2-6 GHz,an instantaneous bandwidth of 4 GHz,a sensitivity of-99dBm,and a dynamic range of 50 dB.This work has important reference value for the design and implementation of two-dimensional silicon-based integrated microwave photonic phased array radar in the future.